A stable and ultrasensitive surface enhanced Raman scattering (SERS) substrate has been fabricated via assembling Au nanoparticle (Au NPs) with different sizes onto the surface of Ni nanocone arrays (Ni NCAs) routed by a two-step electrodeposition method, which is both time and cost effective. The dimension of the Au NPs formed on the Ni NCAs can be controlled by varying the Au deposition time to achieve the best SERS performance. The electromagnetic field on this multilevel hierarchy structure with two different Au NPs sizes was simulated by finite difference time domain method to reveal that hot spots formed by two kind of inter Au NPs gaps have made contributions to the highly enhanced electromagnetic field. This Au NPs-decorated Ni NCAs substrate with the efficient enhancement ability as well as the reproducibility and recyclability has potentials in practical applications of SERS. (C) 2016 The Electrochemical Society. All rights reserved.